1. Field of the Invention
The present invention relates to: an induction heating device serving to apply heat to a heating element of a fuser installed on an image forming apparatus; and an image forming apparatus with this induction heating device being installed thereon.
2. Description of the Related Art
The following description sets forth the inventor's knowledge of related art and problems therein and should not be construed as an admission of knowledge in the prior art.
Some of the image forming apparatuses such as copiers, printers, and facsimiles and the multifunctional digital image forming apparatuses called as MFPs (Multi Function Peripherals), collectively having the functions of these image forming apparatuses, have an induction heating device as a source of heat for heating a heating element of the fuser.
Such an induction heating device conventionally has employed a method of achieving control of power to a heating element of the fuser: performing full-wave rectification to convert a commercial AC voltage to DC and applying it to the induction heating device; and controlling the ON/OFF state of a switching element constituting an IGBT (Insulated Gate Bipolar Transistor) for example, coupled in series with an induction heating coil.
Such an induction heating device is configured to achieve control of power to a heating element of the fuser by the changing the duty ratio of ON and OFF periods of the switching element, more specifically by changing the duty ratio based on a peak value of the input voltage and an value of power needed to heat the heating element to a certain temperature (for example, Japanese Unexamined Patent Publication No. 2003-098860).
Sometimes the voltage of an input commercial alternating current (provided at a frequency of either 50 Hz or 60 Hz) changes while the induction heating device is heating the heating element, and if the input voltage has a high peak value, the switching element, which turns the induction heating coil ON and OFF, can be broken down because of too much input voltage.
A distortion of an input voltage waveform also affects the input power greatly. A distortion of an input voltage waveform is a phenomenon caused by the deterioration of a power generator, which can be commonly found in developing regions of the world. When the input voltage shows a distorted wave, the relationship between the actual effective input voltage Vrms and the peak voltage Vp cannot be expressed by the following formula: Vrms=Vp/√{square root over (2)}, which represents a normal sine wave.
Losing accuracy in controlling the input power when there is a distortion in an input voltage waveform as described above, has been a problem with such a conventional induction heating device configured to achieve control of the input power by changing the duty ratio of ON and OFF periods of the switching element.
The description herein of advantages and disadvantages of various features, embodiments, methods, and apparatus disclosed in other publications is in no way intended to limit the present invention. Indeed, certain features of the invention may be capable of overcoming certain disadvantages, while still retaining some or all of the features, embodiments, methods, and apparatus disclosed therein.